What is a moonphase watch?

A watch with a moon phase display is very popular among watch enthousiasts. Because a watch that shows the current position of the moon not only looks interesting, it also hides a stunningly ingenious technique that is hundreds of years old. But what exactly is a moon phase watch? And why would you choose a moon phase watch? In this blog we explain how this special watch complication works. 

What is a moon phase watch?

A moonphase watch has a window in the dial that shows you the different phases of the moon, exactly as it appears in the sky at that moment. These positions of the moon are called moon phases.

Why a moon phase watch?

In our time of satellites and smartphones we can hardly imagine it anymore, but for centuries, man was depending on the phases of the sun and moon for determining time. Sowing and harvesting crops, religious holidays, and for sailors, determining high and low tide. The ancient Greeks even had a kind of calculator with which they could calculate the positions of the sun, moon and planets.

That is why from the fifteenth century onwards, (astromnomical) clocks were developed to tell the phase of the moon without having to go outside.

You can of course opt for a moonphase watch because you like the look, but the moonphase also has its function today. For example for military operations, outdoor sports and water sports enthousiasts. Although these groups usually opt for a modern digital watch that can accurately predict and display the moonphases and water levels.

What is the difference between a sun and moon watch and a moon phase watch?

In addition to moon phase watches, there are also watches with a sun and moon display in the dial. Such a sun and moon watch only indicates whether it is day or night with the image of a sun or a moon, not the position of the moon.

How does a moon phase watch work?

Mechanical moon phase watch

With an analog mechanical watch, the moon phase is incorporated into the dial. Usually with an image that looks like the appearance of the moon in the sky on a particular night. To achieve this, a 59-tooth gear drives a metal pin that connects to the mechanism of the hour hand, causing it to click forward one notch every 24 hours and shift the moon in the display. This cycle, in turn, follows the 29.53 day lunar cycle.

Wait a minute, 29, 5 days? A month is 30 or 31 days, right? That's right. In practice you will hardly notice this difference, yet a mechanical moon phase - if the watch has been running continuously for 3 years - will be almost 1 day behind. These watches must therefore be manually corrected at regular intervals (to be exact: 2 years, 7 months and two weeks).

Some mechanical watches have a 135-notch sprocket, which only needs to be adjusted once every 122 years. These are very accurate - often handmade - timepieces that we mainly encounter in the top luxury segment.

Analog Quartz Moon Phase Watches

Quartz moon phase watches work much the same as mechanical moon phase watches. If the Quartz moon phase watch also contains a perpetual calendar, it will automatically correct for the deviation between 29, 5 and 30 or 31 days.

Digital moon phase watches

No matter how beautiful an analog moon phase watch looks, if you depend on the exact moon phases, it is better to choose a modern digital watch. The phase of the moon determines the tides. Especially important for boaters. What time the sun rises and sets is important for soldiers and outdoor athletes.

With digital watches, the calendar is usually pre-programmed for 100 years. When you have set your time zone / location correctly - and the watch includes a moon phase or tide display - it will automatically display correctly. Digital watches with GPS or smartphone synchronization are even more accurate.

Which watch you choose depends entirely on what you want to use it for. If you only go sailing occasionally, a simple high tide table may be sufficient. But if you are a semi-professional surfer, extensive tide information is required. The water resistance of a watch also plays a major role.

How do you set a moon phase watch?

Always read the user manual carefully before setting your moon phase watch. Every brand and type of movement has its own setting method. With mechanical watches, there are two ways to set the correct moon phase: via the crown, or via a special push button.

You have to be careful with watches with a moon phase complication, because the mechanism is complex and sensitive. Check whether the watch set to the correct date and time, as the moon phase and the date are linked. 
Before setting the moon phase, pull out the crown. You do this to prevent the movement of the hands from damaging the movement when you set the moon phase. 

1. Then turn the moon disc so that the full moon is in the center of the window. 

2. Look up the current phase of the moon, for example on the site http://www.antique-horology.org/PDAmoon/appmonth.htm

3.  From the current moon phase, count the number of days since the last full moon. 

4. Gently turn the crown one tick (one notch) for each day to move the moon to the correct, current phase. For watches with a push mechanism, you press 1 time per day. 

5. Push the crown back in to its normal position and you're done. 

More Moon phase watches 

Whether you go all out for the aesthetics of a classic moon phase watch or a cutting-edge model, know that there is always a special and advanced technology behind it. Visit our moon phase watch page to find which watch suits you best.

*Source: https://nl.wikipedia.org/wiki/Mechanisme_van_Antikythera